The present invention relates generally to an image apparatus for endoscopes, and specifically to an image apparatus for endoscope systems that can be used for obtaining internal views of, for instance, living bodies, laid-down pipes or the like.
Endoscopes are apparatus used widely in the medical and industrial fields. Especially in the medical field, images obtained via an endoscope inserted through the body cavity are used for diagnosis of affected sites. However, the body cavity often have complicated configurations, and especially in the case of a tract and cavity having folds and protuberances, there are sites hard to see, even when the leading end of the endoscope is bent to turn its viewing direction. For instance, when it comes to the large intestine, difficulty is encountered in viewing its whole area because there are large folds whose backs are hard to see.
One possible approach is to have a wide-angle optical system thereby widening the range to be viewed. This would ensure that the leading end of the endoscope is slightly bent to implement a wider range of viewing.
However, the wide-angle optical system is generally likely to produce distortion by which objects on the periphery of a screen are reduced and seen distorted. Although that distortion may be corrected by optical design, there are increases in the number of lenses and lens diameter. This is unsuitable for use with very small apparatus such as endoscopes, imposing some limitations.
Therefore, methods for correction of distortion by image processing have been proposed, as set forth in Patent Publications 1, 2 and 3.
A method for changing the amount of correction of distortion is also set forth in Patent Publication 4.
Patent Publication 1: JP(A) 2005-110207
Patent Publication 2: JP(A) 2007-38856
Patent Publication 3: JP(A) 2007-124088
Patent Publication 4: JP(A) 11-275444
However, these prior arts have the following problems.
Patent Publication 1 shows that with an eye on how the periphery of a screen is seen, distortion control is implemented mainly with lenses. It also shows that distortion is changed by image processing, but it does not take care of how much images on the periphery of the screen are seen by image processing because correction is implemented in the direction of enlarging images on the center and reducing images on the periphery. Although there are no specific lens data, this arrangement unavoidably leads to increases in the size of the optical system: it cannot be used with endoscopes in view of size reductions.
Likewise, Patent Publication 2 pays attention to images on the periphery of the screen, but says nothing specific about lenses or image processing; in other words, it remains to be seen whether that is viable or not.
The prior art set forth in Patent Publications 1 and 2 is used in onboard applications, and has for its object to optimize distortion depending on how it is mounted on a car; that is, it has difficulty in immediate application to endoscopes.
The prior art of Patent Publication 3 is designed such that correction of distortion by image processing is applied to endoscopes. However, the object is to correct images for detection of subjects; so distortion of lenses is merely corrected. Therefore, there is no consideration of how images the periphery are seen at best.
The prior art of Patent Publication 4 uses a changeover switch to, or not to, implement correction of distortion, and is going to be used with cameras. For this reason, when it is used on a wide-angle optical system having large distortion such as that for an endoscope, there is a very large change in images depending on whether or not the correction is implemented, which may rather render viewing very difficult.
These prior arts gain control of distortion, but say nothing about how the complicated morphologies of the inside of the living body are viewed, and about the construction of distortion best suited for viewing through an endoscope as well.